Continuous apparatus for extruding and forming thermoplastic articles

ABSTRACT

Apparatus for extruding a sheet of foamed thermoplastic material having an expanded, cellular, inner structure and a thin, unexpanded, molecularly integrated skin of the same material covering at least one side thereof, and, without interruption, forming thermoplastic articles therefrom. The skin is formed by controlling the temperature of the desired surface of a foamable thermoplastic sheet immediately after it is extruded so as to prevent the expanding and foaming of said surface.

United States Patent Thomas W. Winstead 2 Overlook Lane, Baltimore, Md.21210 864,294

Oct. 3, 1969 Jan. 4, 1972 Continuation of application Ser. No. 729,856,Apr. 2, 1968, now abandoned which is a division of application Ser. No.508,417, Nov. 18, 1965, now abandoned. This application Oct. 3, 1969,Ser. No. 864,294

lnventor Appl. No. Filed Patented CONTINUOUS APPARATUS FOR EXTRUDING ANDFORMING THERMOPLASTIC ARTICLES 9 Claims, 3 Drawing Figs.

US. Cl 425/326, 425/4, 425/243, 425/294, 425/385, 264/54, 425/ 3 88 Int.Cl B29d 23/03 Field of Search ..18/2 W, 4 S,

[56] References Cited UNITED STATES PATENTS 3,091,808 6/1963 Dakin 18/19F 3,111,714 11/1963 Branscum... l8/D1G. 55 3,234,594 2/1966 Winstead....18/12 M 3,331,103 7/1967 Fox 18/14S 3,431,163 3/1969 Gilbert 18/5 P XPrimary Examinerl-l. A. Kilby, Jr. AttorneyRaphael Semmes ABSTRACT:Apparatus for extruding a sheet of foamed ther moplastic material havingan expanded, cellular, inner structure and a thin, unexpanded,molecularly integrated skin of the same material covering at least oneside thereof, and, without interruption, forming thermoplastic articlestherefrom. The skin is formed by controlling the temperature of thedesired surface of a foamable thermoplastic sheet immediately after itis extruded so as to prevent the expanding and foaming of said surface.

rmmcnm 4m 3.6321266 INVENTOR THOMAS hf WINSTEAD BY RM TTOR/VEYCONTINUOUS APPARATUS FOR EXTRUDING AND FORMING THERMOPLASTIC ARTICLESThis application is a continuation of Ser. No. 729,856, filed Apr. 2,1968, now abandoned, which is a division of application Ser. No.508,417, filed Nov. 18, 1965, now abandoned, for Continuous Method andApparatus For Extruding and Forming Thermoplastic Articles.

This invention relates to a continuous apparatus for extruding foamedthermoplastic material, and, without interruption, forming thermoplasticarticles therefrom. More particularly, the invention consists in new anduseful improvements in such a continuous apparatus designed to providefoamed thermoplastic articles, such as trays or the like, from anextrudate having an expanded, cellular, inner structure and a relativelythin, unexpanded skin of the same material, molecularly integral withthe expanded structure, covering at least one surface of the extrudateor selected areas thereof for reinforcing and stiffening purposes.

In my copending application Ser. No. 475,734, filed July 29, 1965, nowU.S. Pat. No. 3,887,328, issued June 11, 1968, I described an apparatusfor extruding foamed thermoplastic sheets in such a manner as to insurea uniform distribution of pressure flow at all points along the die lipto thereby eliminate strains or distortions in the extrudate and toaccommodate the maximum widthwise expansion of the extrudate to preventthe formation of wrinkles thereon.

In another copending application Ser. No. 480,917, filed Aug. 19, 1965,now U.S. Pat. No. 3,479,694, issued Nov. 25, 1969, I described acontinuous, integrated system for the manufacture of formed articlesfrom foamed or cellular thermoplastics, preferably, but not necessarily,embodying an extrusion method and apparatus, such as described in mycopending application Ser. No. 475,734, previously referred to.

In a still further copending application Ser. No. 506,805, filed Nov. 8,1965, now U.S. Pat. No. 3,461,496, issued Aug. 19, 1969, I described amethod and apparatus for extruding a sheet or tube of thermoplasticmaterial having an expanded, cellular, inner structure and a relativelythin, unexpanded skin of the same material, molecularly integral withthe expanded structure, covering at least one surface of the extrudate.

The present invention, therefore, resides in a unique combination ofcertain features of my copending applications above referred to toprovide a continuous, uninterrupted apparatus for producing formedthermoplastic articles of foamed material and having one or bothsurfaces thereof coated with an integral skin of the same material orhaving selected areas of such surfaces thus coated. My previouslydescribed technique for forming skins or cellular thermoplasticextrudates was directed primarily to forming extrudates which are notimmediately embodied in shaped article. However, this technique isparticularly advantageous for producing an extrudate, and, then, withoutinterruption, forming the final article with a skin on one or bothsurfaces or on selected areas of such surfaces.

Carefully controlled conditions are required for forming foamed articlesfrom a previously extruded thermoplastic sheet, for example, where it isnecessary to reheat the sheet and then form it by any one of the varioustherrnoforrning techniques currently used to produce articles fromthermoplastic sheeting. It is not always possible to achieve theparticular properties one desires utilizing conventional techniques. Forexample, where an orientated styrene film or sheet is laminated to afoam substrate, the orientation is considerably reduced or destroyedwhen the sheet is reheated sufficiently to permit adequate thermoformingoperations. This is particularly true if deep draws are required to formthe article. Another difficulty in conventional techniques results fromthe fact that the density of the foam is frequently adversely affectedwhile the composite laminate is being heated, since the heat absorptionand heat capacity of the nonfoamed skin is quite different from that ofthe foamed substrate. Perhaps most important of all is the fact that theconventional methods are twostep processes which require, first, thecareful preparation of the composite sheet, and, second, the rathercritical reheating and forming operation.

It is therefore an object of the present invention to provide apparatuswhereby foamed articles having skin on one or both surfaces can beproduced in an economical, continuous, uninterrupted process.

Another object resides in the provision of apparatus in which the skindoes not seriously limit the depth to which the formed articles may bedrawn.

A further object is to provide means for producing articles ofcontrolled density cores and controlled thickness skins in whichorientation has been established and yet not lost during the formingoperation.

A still further object of the invention is to provide a continuous,uninterrupted apparatus for forming skincoated articles of thermoplasticwherein the forming operation takes place as soon as possible afterextrusion so as to utilize residual heat of extrusion and obviate thedifiiculties encountered in reheating the extrudate.

With the above and other objects in view which will appear as thedescription proceeds, the invention consists in the novel featuresherein set forth, illustrated in the accompanying drawings, and moreparticularly pointed out in the appended claims.

Referring to the drawings in which numerals of like character designatesimilar parts in all views:

FIG. 1 is a sectional view of one form of extruder head such ascontemplated by the present invention;

FIG. 2 is a diagrammatic view illustrating the combination of one formof extruder diehead with the forming apparatus; and

FIG. 3 illustrates a modified extruder head.

The invention may be carried out with the use of extrusion dies ofvarious types and configurations, provided they are equipped adjacenttheir extrusion orifices with suitable means for chilling at least onesurface of the extrudate to prevent expansion of said surface and form askin as described in my copending application, above referred to, Ser.No. 506,805, filed Nov. 8, 1965. For illustrative purposes, the presentinvention will be described as embodying a diehead such as illustratedin FIG. 1 of said copending application.

Referring to FIG. I of the drawings, 5 represents an extruder bodyhaving a longitudinally extending central passageway 6 fed from asuitable source of molten plastic (not shown). The discharge end of thepassageway or barrel 6 passes through an extruder head 7 and preferablyterminates in communication with a converging inlet port 8 locatedcentrally of a circular die lip 9. An end cap 10, also circular inshape, registers with the die lip 9 and is secured in place by anysuitable means, and the inner face of this end cap is conically recessedas at 11, providing a feed chamber 12 which is coaxial with thepassageway 6 and converging opening 8. This chamber has divergingsidewalls which terminate in slightly axially and inwardly spacedrelation to the periphery of the end cap 10. An adapter 13 conformssubstantially to the surface contour of the chamber 12, with theexception that the upper portion thereof is provided with a V- shapedcutout area which, when the adapter is installed, provides divergingradial confines for the chamber 12, providing a substantially fanshapedreservoir of which the upper portion of the circular lip 9 forms theopposite wall, all as shown in my said copend ing application Ser. No.475,734.

Also, as described in my said copending application, to facilitate thecontrol of the extrudate after leaving the die lips, a mandrel 14 isprovided adjacent the die lips. This mandrel preferably comprises avertically disposed, transversely arcu= ate tube which is supported inan upright position so that as the extrudate 15 leaves the die lips, itis spread laterally and supported so as to provide a maximum possibleaccommodation of the widthwise expansion of the extrudate.

In applying the surface cooling means of the present invention to thistype of extrusion head, an arcuate housing 16 is mounted immediatelyadjacent the discharge orifice from the extrusion chamber 12a. Thehousing is fed through tube 17 from a suitable source of cooled air orgas (not shown), and preferably converges at its discharge end to forman arcuate discharge slot 18 which is directed against the adjacentsurface of the extrudate 15. Preferably, a baffle 19 115 provided in thehousing 16 to facilitate uniformity of the flow of the cooling medium.As the extrudate progresses from the extrusion chamber 12a, it expandsrapidly. However, the surface which has been chilled to the desireddegree remains unexpanded and provides an integral skin 15a, thethickness of which is directly controlled by the degree of cooling whichhas been provided through means of the cooling housing 16. While theskin stretches laterally, it does not undergo a threedimensionalexpansion and remains as a molecularly integral covering for theunderlying foamed resin H5. The skin covered extrudate 15-l5a is thenprocessed in the forming apparatus illustrated in FIG. 2 to produce avariety of foamed plastic articles.

It may be pointed out that the slot 18 is designed to facilitate thedischarge of a high velocity, uniform flow of air or other cooling gasupon the adjacent surface of the extrudate to form the desired skin. Theamount of gas, its rate of flow, temperature, and the rate of extrusionare all variables contributing to the thickness of the skin.

Preferably, an air space 16a is provided between the housing 16 and theextrusion head to maintain the proper cooling temperature in the housingand to avoid cooling the extruder head and die.

Referring to FIG. 2 which diagrammatically illustrates the integratedsystem, an expandible thermoplastic material is extruded through thediehead 7, forming a continuous thermoplastic strip or sheet 15, havinga skin coating on one or both of its surfaces. The sheet travels overthe spreading yoke 14 from which it is conducted around the periphery ofa forming wheel 20 of the type shown in my copending application Ser.No. 480,917 now U.S. Pat. No. 3,479,694 issued Nov. 25, 1969 whichvacuum forms the articles 21 on the sheet 15. By sequential valvingdescribed in my said copending application, the vacuum is applied to thesuccessive molds on the forming wheel as the sheet 15 is tangent to therespective flat faces on the underside of the forming wheel and afterthe sheet has been flattened and stretched by the spreading yoke 14.

The formed articles, while still carried by the sheet 15, are thenstripped tangentially from the upper side of the forming wheel and thesheet and articles are conducted to the cutting unit 22 where the formedarticles are removed from the sheet and directed to a stacking unit (notshown). The remaining selvage of sheet 15 is thereupon conducted to agranulating machine by means of the reverse guide rolls 23, all asdescribed in my said copending application Ser. No. 480,917.

Air cooling means, such as diagrammatically shown at 24 and 25, may bedirected against the indicated means of the sheet passing over theforming wheel 20 to facilitate the forming operation.

The combination of the present invention is not limited to the inclusionof a die structure such as shown in FIG. 1 for illustrative purposes,but may be of the type having straight die lips for extruding a flatsheet or circular die lips for extruding a tubular extrudate. Theimportant feature resides in conducting the extruded sheet with itscovering skin or skins directly to the forming operation immediatelyafter extrusion so as to utilize the heat of extrusion to render thethermoplastic formable.

Another feature of the invention, where desirable, is that bycontrolling the cooling pattern of the cooling medium discharged throughthe housing 16 (FIG. 1) or other cooling unit and applying the coolingmedium to selected areas of a surface of the extrudate where it isdesirable to produce skin effects, it is perfectly feasible to produce acheckerboard effect in which every other space incorporates a skin ofsignificant thickness with normal cell surfaces in between the spaces.Also, it is possible to form skins on selected areas only by controllingthe interval of application of the cooling effect timewise in relationto the rate of extrusion.

As indicated in my copending application Ser. No. 506,805, now U.S. Pat.No. 3,461,496 issued Aug. 19, 1969, the cooling of the surface orsurfaces of the extrudate may be effected by conductive cooling or byconvective cooling, and in the former case it is preferable to coat theconductive cooling surfaces with an antifriction material such aspolytetrafluorethylene.

In the embodiment of the die shown in FIG. I, the cooling space 16a isrelied upon to insulate the extrusion head from the cooling unit. Thismay also be accomplished by providing a thermal barrier between thesetwo units. It is important that this thermal barrier or the insulatingair space be sufficiently effective to maintain a sharp temperaturegradient between the lips of the die and the skin producing element. Atypical temperature profile would be to maintain the die body 7 atapproximately the same temperature as the extrusion stock, for example300 F. While the cooling unit 16 and the cooling medium is maintained ata temperature of perhaps 0 F.

As previously indicated, the chilling of the surface of the extrudatemay also be effected by conduction cooling means. For example, in FIG. 3the discharge end of the extrusion head 7 is provided with an annularcooling ring 32 having passageways 33 for conducting a cooling fluid.This device includes insulating blocks 31 between the extrusion head andthe ring 32 to maintain the full effect of the cooling medium withoutcooling the extrusion head.

In this form of the invention, a diverging, annular mouth 34communicates directly with the discharge end of the extrusion orifice8a, and, as the extrudate 15 passes through the mouth, both surfaces arecooled to the desired degree by the cooling effect of the ring 32, thusproviding an extrudate with integral, unexpanded skins 15a and 15b onopposite surfaces thereof. Here again, if a skin covering is desired ononly one surface of the extrudate, only one of the cooling passageways33 is put into use.

Preferably, the conductive surface or surfaces of the mouth 34 arecoated with polytetrafluorethylene or a similar low friction coatingwhich will not materially inhibit heat transfer.

The divergence of the mouth 34 permits some expansion of the extrudateeven as its surface is being chilled. However, a Hat mouth or apartially flat and partially divergent mouth may be employed.

It is to be noted that this invention may be carried out not only inaccordance with the invention disclosed in application Ser. No. 480,917,now U.S. Pat. No. 3,479,694, issued Nov. 25, 1969, but also inaccordance with any technique where forming is employed immediatelyafter extrusion and the heat of extrusion is relied upon to render thethermoplastic formable. Also to be noted is that the thickness of theouter skin, as well as the density of the expanded inner structure ofthe extrudate, may be readily controlled by this invention.

Further to be noted is that in the case where a soluble blowing agent isemployed, an additional advantage of the method of this invention over atwostep process where the extrudate is reheated in order to be formed isthat the blowing agent has not had time to escape and is still retainedduring the forming operation to further enhance the formability of thesheet due to its plasticizing effect. Also, in the application of thisinvention to extrudates containing soluble blowing agents the maximumorientation can be achieved in both the skin as well as the cell wallsthemselves. Orientation of the skin takes place as a result of thebiaxial stretching of the extrudate as it emerges from the die andexpands, and orientation of the cells takes place as a result of theblowing agent within each cell being under pressure at the time offorming and before the blowing agent escapes.

From the foregoing, it is believed that the invention may be readilyunderstood by those skilled in the art without further description, itbeing borne in mind that numerous changes may be made in the detailsdisclosed without departing from the spirit of the invention as setforth in the following claims.

I claim:

1. Apparatus for continuously manufacturing articles having an expandedinner structure of foamed thermoplastic extrudate and an unexpanded skinof said extrudate molecularly integral with at least one surface of theinner structure, said apparatus comprising a diehead assembly, apassageway in said assembly for feeding molten plastic having a foamingagent, said passageway communicating at its discharge end with die lipsproviding an elongated die orifice arcuate in a plane parallel to thewidth of the extrudate, means immediately posterior to said die orifice,disposed along at least one side thereof, for chilling the adjacentsurface of extrudate as it emerges from said orifice to preventexpansion of the extrudate at said surface and form a molecularlyintegral, noncellular skin thereon, means to prevent chilling of saiddiehead and the lips of said die orifice, means posterior to saiddiehead assembly for laterally spreading the extrudate, and a moldingassembly disposed closely posterior to said spreading means forreceiving the spread extrudate, said spreading means comprising a yokeof arcuate contour substantially concentric to the axis of said dieorifice, located in substantially the same plane as said orifice, andradially spaced therefrom a distance which is calculated to accommodatethe transverse expansion of said extrudate after it leaves said orifice.

2. Apparatus as claimed in claim 1, wherein said chilling meanscomprises convective cooling means.

3. Apparatus as claimed in claim 1, wherein said chilling meanscomprises conductive cooling means.

4. Apparatus as claimed in claim 3, wherein said conductive coolingmeans has a conducting cooling surface coated with an antifrictionmaterial.

5. Apparatus as claimed in claim 1, wherein said molding assemblycomprises a vacuum molding unit. I

6. Apparatus as claimed in claim 5, wherein said molding unit comprisesa rotatable forming wheel having a series of vacuum molds on itsperiphery.

7. Apparatus as claimed in claim 1, wherein said passageway has aportion which diverges to the opposite ends of said die lips.

8. Apparatus for continuously manufacturing articles having an expandedinner structure of foamed thermoplastic extrudate and an unexpanded skinof said extrudate molecularly integral with at least one surface of theinner structure, said apparatus comprising a diehead assembly, apassageway in said assembly for feeding molten plastic having a foamingagent, said passageway communicating at its discharge end with die lipsproviding an elongated die orifice arcuate in a plane parallel to thewidth of the extrudate, means immediately posterior to said die orifice,disposed along at least one side thereof, for chilling the adjacentsurface of extrudate as it emerges from said orifice to preventexpansion of the extrudate at said surface and form a molecularlyintegral, noncellular skin thereon, means to prevent chilling of saiddiehead and the lips of said die orifice, and a molding assemblydisposed closely posterior to said chilling means for receiving theextrudate.

9. Apparatus as claimed in claim 8, wherein said passageway has aportion which diverges to the opposite ends of said die lips.

1. Apparatus for continuously manufacturing articles having an expandedinner structure of foamed thermoplastic extrudate and an unexpanded skinof said extrudate molecularly integral with at least one surface of theinner structure, said apparatus comprising a diehead assembly, apassageway in said assembly for feeding molten plastic having a foamingagent, said passageway communicating at its discharge end with die lipsproviding an elongated die orifice arcuate in a plane parallel to thewidth of the extrudate, means immediately posterior to said die orifice,disposed along at least one side thereof, for chilling the adjacentsurface of extrudate as it emerges from said orifice to preventexpansion of the extrudate at said surface and form a molecularlyintegral, noncellular skin thereon, means to prevent chilling of saiddiehead and the lips of said die orifice, means posterior to saiddiehead assembly for laterally spreading the extrudate, and a moldingassembly disposed closely posterior to said spreading means forreceiving the spread extrudate, said spreading means comprising a yokeof arcuate contour substantially concentric to the axis of said dieorifice, located in substantially the same plane as said orifice, andradially spaced therefrom a distance which is calculated to accommodatethe transverse expansion of said extrudate after it leaves said orifice.2. Apparatus as claimed in claim 1, wherein said chilling meanscomprises convective cooling means.
 3. Apparatus as claimed in claim 1,wherein said chilling means comprises conductive cooling means. 4.Apparatus as claimed in claim 3, wherein said conductive cooling meanshas a conducting cooling surface coated with an antifriction material.5. Apparatus as claimed in claim 1, wherein said molding assemblycomprises a vacuum molding unit.
 6. Apparatus as claimed in claim 5,wherein said molding unit comprises a rotatable forming wheel having aseries of vacuum molds on its periphery.
 7. Apparatus as claimed inclaim 1, wherein said passageway has a portion which diverges to theopposite ends of said die lips.
 8. Apparatus for continuouslymanufacturing articles having an expanded inner structure of foamedthermoplastic extrudate and an unexpanded skin of said extrudatemolecularly integral with at least one surface of the inner structure,said apparatus comprising a diehead assembly, a passageway in saidassembly for feeding molten plastic having a foaming agent, saidpassageway communicating at its discharge end with die lips providing anelongated die orifice arcuate in a plane parallel to the width of theextrudate, means immediately posterior to said die orifice, disposedalong at least one side thereof, for chilling the adjacent surface ofextrudate as it emerges from said orifice to prevent expansion of theextrudate at said surface and form a molecularly integral, noncellularskin thereon, means to prevent chilling of said diehead and the lips ofsaid die orifice, and a molding assembly disposed closely posterior tosaid chilling means for receiving the extrudate.
 9. Apparatus as claimedin claim 8, wherein said passageway has a portion which diverges to theopposite ends of said die lips.